1. Field of the Invention
This invention relates to a device for adjusting the flow rate of air or air-fuel-mixture drawn into an internal combustion engine during idling.
2. Description of the Prior Art
Internal combustion engines usually have an auxiliary air passage which bypass the engine throttle valve. The auxiliary passage permits air to be drawn into the engine when the throttle valve is closed. A screw is located in the auxiliary passage to adjust the effective cross-sectional area thereof to determine the flow rate of air drawn into the engine during idling.
The engines usually have positive crankcase ventilation (PCV) and exhaust gas recirculation (EGR) systems for emission control. These systems inevitably discharge contaminants, such as oil or carbon particles, into the fresh air drawn into the engine. In addition, some dirt passes through the intake air filter or cleaner and is entrained with engine intake air.
When contaminants or dirt accumulate on the idle adjusting screw, the effective cross-sectional area of the auxiliary passage decreases from its nominal value, reducing the flow rate of air into the engine during idling. This causes a reduction in the engine rotational speed during idling. Conventional idle adjusting screws have been unsatisfactory from the standpoint of their ability to prevent contaminants or dirt from adhering thereto and accumulating thereon.